Ba(OH) Sub 2 .8H sub 2 O Process for the Removal and Immobilization of Carbon-14. Final Report

摘要

The airborne release of sup 14 C from various nuclear facilities has been identified as a potential biohazard due to the long half-life of sup 14 C (5730 years) and the ease with which it may be assimilated into the biosphere. At ORNL, technology has been developed for the removal and immobilization of this radionuclide. Prior studies have indicated that sup 14 C will likely exist in the oxidized form as CO sub 2 and will contribute slightly to the bulk CO sub 2 concentration of the gas stream, which is air-like in nature (approx.300 ppM/sub v/ CO sub 2 ). The technology that has been developed utilizes the CO sub 2 -Ba(OH) sub 2 .8H sub 2 O gas-solid reaction with the mode of gas-solid contacting being a fixed bed. The product, BaCO sub 3 , possesses excellent thermal and chemical stability, prerequisites for the long-term disposal of nuclear wastes. For optimal process operation, studies have indicated that an operating window of adequate size does exist. When operating within the window, high CO sub 2 removal efficiency (effluent concentrations <100 ppB/sub v/), high reactant utilization (>99%), and an acceptable pressure drop across the bed (3 kPa/m at a superficial velocity of 13 cm/s) are possible. Three areas of experimental investigation are reported: (1) microscale studies on 150-mg samples to provide information concerning surface properties, kinetics, and equilibrium vapor pressures; (2) macroscale studies on large fixed beds (4.2 kg of reactant) to determine the effects of humidity, temperature, and gas flow rate upon bed pressure drop and CO sub 2 breakthrough; and (3) design, construction, and operation of a pilot unit capable of continuously processing a 34-m exp 3 /h (20-ft exp 3 /min) air-based gas stream. (ERA citation 11:019236)